UDP-glucuronosyltransferase (UDPGTase) is one of the enzymes which plays an important role in the conjugation and excretion of biotransformational products in detoxification processes. In order to study the functional role of UDPGTase in these processes, we are preparing a library of monoclonal antibodies (MAbs) to the human UDPGTase. Female Balb/c mice were immunized with chemically synthesized peptides of 20 amino acid residues (UDPGTase 394 - 413) which are essential for UDPGTase activity. The peptides were conjugated with KLH prior to immunization. Six independent hybridomas were generated by the fusion of myeloma cells with spleen cells from mice immunized with the chemically synthesized peptides. One of the hybridomas produced IgGI type of MAbs and five hybridomas produced IgM types. All MAbs of each type in culture fluids bound to the immunogen in RIA but not more than 3 times that for nonspecific MAbs. No immunoprecipiton occurred between the MAbs and the peptides in Ouchterlony double immunodiffusion analysis. The library of MAbs to the peptides would be useful for the determination of amino acid sequences which are essential for UDPGTase activity, and also for identification, reaction phenotyping and quantification of UDPGTase in different organs and tissues of humans.